CRYPTIC EXPRESSION OF THE 70-KDA HEAT-SHOCK-PROTEIN, HSP72, IN GERBILHIPPOCAMPUS AFTER TRANSIENT ISCHEMIA

The 70 kDa heat shock protein, hsp72, is known to be induced following transient global ischemia in brain, as detected by immunocytochemistr y and in situ hybridization techniques. However, while hsp72 mRNA is e xpressed rapidly following postischemic recirculation, immunocytochemi stry fails to detect hsp72 protein for many hours after such insults, even in cell populations that readily express Fos and other proteins e ncoded by ischemia-induced mRNAs. In the present study, hsp72 expressi on in gerbil hippocampus was compared by immunocytochemistry and immun oblot methods at several intervals following 10 min ischemia. As estab lished in previous studies, hsp72 immunoreactivity remained undetectab le in postischemic neurons at 6 h following such insults. In contrast, immunoblots of dissected gerbil hippocampus demonstrated nearly maxim al accumulation of hsp72 at this time point. These results indicate th at the protein is present, but cryptic to detection in perfusion-fixed sections, during early recirculation. The constitutively expressed he at shock cognate protein, hsc70, did not show significant changes in l evel or distribution by either method, except for a decrease in CA1 st aining at 48 h. These results confirm that hsp72 rapidly accumulates t o high levels in postischemic hippocampus, and suggest that further st udies of its subcellular localization during this interval may offer i nsight into its functional role as a component of the stress response in neurons after such insults.